The invention relates to a holding device for locking the head of a syringe piston on a syringe pump pusher, the device being equipped with arms integral each with a pinion pivotable about its axis and movable in translation so as to drive the corresponding arm in a same movement between a rest position, in which the arms are “closed” and “pressed” against the pusher, and an open position, in which the arms are “opened” and “removed” from the pusher, the translation being performed before the rotation during the movement toward the open position, or in reverse order toward the rest position, the holding device further comprising a control member and means for converting a portion of the movement of the control member by transmitting it to at least one pinion in the form of a translation movement and means for converting a portion of the movement of the control member by transmitting it to at least one pinion in the form of a rotation movement.
Syringe pumps are often used in the medical field. These syringe pumps are constituted essentially by a device for immobilizing the cylinder of the syringe and a device for pushing the piston in the cylinder at a defined speed in order to supply the solution to the patient in a controlled manner. Further, it is preferable that the piston head be held against the pusher of the syringe pump to avoid a siphoning phenomenon. It happens sometimes that a depression forms downstream of the syringe. If the piston head is not held, there is a risk that the syringe will empty itself partially or completely and will thus supply the therapeutic solution to the patient at a much too high rate, which can have tragic consequences.
Various solutions have been proposed. For example, a hand-actuated holding device is known from document EP 1 279 410 A1, which device comprises an element mobile perpendicularly to the axis of the syringe. This mobile element is crescent-shaped with a V-shaped slot located in the inner arc of the crescent. By returning the mobile element against the pump housing, the edge of the piston head penetrates into the V-shaped slot, which then holds it against the pusher. This solution requires that the syringe head be aligned with the V-shaped slot of the mobile element.
In another common solution, the holding means are constituted by two arms. These arms, which are parallel to the syringe piston head, are mounted on pivoting axes that are parallel to the main axis of the syringe. When the syringe is placed in the syringe pusher, these arms are moved away from each other by pivoting them towards the outside, the piston head is placed against the pusher and the arms are released so that they return to a closed position, thus locking the piston head between them and the pusher.
By themselves, the arms can lock efficiently only syringe heads that have a defined thickness. In other words, the corresponding syringe pumps can be used only for a type of syringe or syringes from a single manufacturer, provided these syringes all have piston heads of the same thickness. Using these pivoting arms with thicker piston heads is not possible, as the arms cannot return to the closed position, and using them with thinner piston heads is dangerous, to the extent that even a very small siphoning effect can have serious consequences, in particular for solutions supplied at a very small rate.
Thus, arms exist that, not only pivot to open, but also carry out a translation movement along the axis of the syringe, so that they can adjust to the thickness of the piston head. Pushing on a lever triggers, first, the translation of these arms, which tends to move them away from the pusher, and then, a rotation movement of the arms, which tends to rotate them toward the outside while moving them away from each other. Once the piston head is placed against the pusher, the lever is released, the arms close again until they touch the syringe piston rod, then they move back toward the pusher until they touch the syringe piston head.
Such a holding device is known, for example, from document U.S. Pat. No. 6,428,509 B1. This device comprises a first pivoting mechanism that drives the arms in rotation and a second mechanism that drives the arms in translation. The pivoting mechanism is constituted essentially by three toothed wheels placed in series, the first toothed wheel transmitting the rotation movement of the actuating lever to a second toothed wheel, which is integral with the first arm, and the second toothed wheel transmitting in turn the rotation movement to a third toothed wheel integral with the second arm. In the translation mechanism, the rotation axes of the arms are pushed against an actuating plate that has on a protrusion on its other face. The actuating lever is integral with a control plate having a ramp, the protrusion of the actuating plate being supported on the control plate on the side of the ramp. When the lever pivots, this control plate moves until the protrusion slides against the ramp, thus triggering the downward movement of the actuating plate, and as a result, the translation of the arms away from the pusher. A hook locks the actuating plate when it reaches a certain distance, so that it is locked in this position without being able of moving backward again. When the actuating lever is moved back again, the arms close again. The hook that holds the actuating plate is released only during the last degrees of the pivoting movement of the lever, which enables the plate to move back toward the pusher, thus driving the arms along in the same movement. This device is particularly complex and requires a high number of parts.
Another holding device is known from document EP 1 066 846 A1, which device has arms that are pivotable and movable in translation. Each arm is mounted on an axis carrying each a toothed wheel equipped with a central radial groove. A toothed wheel, connected indirectly to an electric motor, is equipped with a central radial projection. This driving toothed wheel is intended to cooperate with the toothed wheel of the first arm, wherein the radial projection of the first toothed wheel projects into the central radial groove of the second. The driving toothed wheel cooperates also with a transmission toothed wheel that transmits the rotation movement of the driving wheel to the toothed wheel of the second arm. The toothed wheel of the second arm is positioned such that the radial projection of the driving toothed wheel also projects into its central radial groove, without meshing, however. Further, the driving toothed wheel is mounted on a ring equipped with an inner thread. The ring it itself mounted on a hollow rod having an outside thread and carrying at one of its ends a toothed wheel that cooperates with the motor. A rod having a flange at one of its ends has its free end projecting into the hollow rod, on the side opposed to the toothed wheel that cooperates with the motor. This rod is free in rotation in the hollow rod while being locked in translation. This assembly enables the driving toothed wheel to move in translation, thus driving the toothed wheels of the arms along in the same movement because the radial projection projects into the radial grooves of the toothed wheels of the arms. The translation movement is limited, on one side, by the toothed wheel that cooperates with the motor, and on the other side, by the flange. A group of springs promotes the translation of the driving wheel to the detriment of its rotation, which is triggered only when the driving wheel can no longer move in translation. Here also, the mechanism requires a high number of parts and its design is particularly complex.
Further, a holding device for the syringe cylinder is known from document US 2004/0116893 A1, which device provides, in one of its variants, three arms pivotable in a radial plane toward the center of the adapter. However, these arms are not movable in the axial direction.